Method and apparatus for scanning recording carriers by means of radiation beams

ABSTRACT

For playing back signals, such as video signals, which are stored on a transparent disc-shaped carrier having deformations on its surface that correspond to the pattern of the signal amplitudes and that are produced by means of a pressing process similar to that employed for a phonograph record, the deformations are scanned by means of a light beam which strikes the deformations as the carrier moves relative to a light source, and the beam is deflected, according to the deformations, as it travels through the carrier to a photoreceiver and associated half plane aperture. The light used for scanning is formed in a very narrow beam of radiation which is narrower than the wavelength of the highest recorded frequency and this is achieved through the use of a slit aperture in the path of the light beam.

I I United States Patent 1191 1111 3,764,759 Herriger et al. Oct. 9, 1973 [54] METHOD AND APPARATUS FOR 1,917,003 7/1933 Williams 179/100.41 1.

SCANNING RECORDING CARRIERS BY 1,951,198 3/1934 Mittell et a1. MEANS OF RADIATION BEAMS 1,956,626 5/1934 Robbins 274/4l.6 R

[75] inventors: Felix l-lerriger, Ulm/Donau;

Gerhard Dickopp, Berlin, both of Germany Licentia Patent-Verwaltungs-G.m.b.H., Frankfurt, Germany Filed: Nov. 16, 1970 Appl. No.2 89,692

[73] Assignee:

Foreign Application Priority Data Nov. 15, 1969 Germany P 19 58858.0

[56] References Cited UNITED STATES PATENTS 2,497,142 2/1950 Shepherd 179/100.4T

AttorneySpencer & Kaye [57] ABSTRACT For playing back signals, such as video signals, which are stored on a transparent disc-shaped carrier having deformations on its surface that correspond to the pattern of the signal amplitudes and that are produced by means of a pressing process similar to that employed for a phonograph record, the deformations are scanned by means of a light beam which strikes the deformations as the carrier moves relative to a light source, and the beam is deflected, according to the deformations, as it travels through the carrier to a photoreceiver and associated half plane aperture. The light used for scanning is formed in a very narrow beam of radiation which is narrower than the wavelength of the highest recorded frequency and this is achieved through the use of a slit aperture in the path of the light beam.

9 Claims, 13 Drawing Figures PATENTED DU 973 SHEET 10F 2 FIG. lb

FIG. 36

FIG. /c

Inventors. Felix Herriger Gerhard D lCkQpp a' W ATTORNEYS BYW PATENTEDBBT 91w 3.764.759

SHEET 2 BF 2 Inventors. Feiix Herriger Gerhard Dickopp BY e ATTORNEYS 1 METHOD AND APPARATUS FOR SCANNING RECORDING CARRIERS BY MEANS 'OF RADIATION BEAMS BACKGROUND OF THE INVENTION The present invention relates to the playing back of signals recorded in the form of spatial deformations on a disc surface by means of a light beam or another radiation beam.

Methods for scanning recording carriers by means of light radiation or similar radiation are known. This generally involves a recording technique in which the signal pattern is constituted by areas which are darkened,

or rendered opaque, to different degrees, or by a dark area of constant depth and variable width having the form of a variable-area track. The quantity of light reflected from or passing through the carrier depends on the degree of darkening of the carrier portions scanned by the reading beam and is used to excite a light receiver whose electric output signal constitutes a reproduction of the recorded signal.

The disadvantage of these techniques is that copies of the -carrier can be obtained only by photochemical or similar processes but not by simple stamping or pressing processes as used for phonograph records.

Also known is a technique for playing back sound recordin'gs engraved in phonograph records by directing a beam of light against the sound groove and converting the light reflected therefrom into corresponding electrical fluctuations by means of a photoelectric system. Use is here made 'of the intensity variations o'fthe reflected light beam which are created, for example in the case of a hill-and-dale, or vertical, recording, the groove area being struck by the beam moves relative to the focal plane of the lens of the light source when the sound carrier moves, and is usually spaced from that focal plane. This constitutes a substantial loss of light and thus poor optical efficiency.

Another method for playing back stored signals employes a carrier whose surface is provided with deformations which correspond to the time pattern of the signal amplitudes. Those deformations are evaluated by means'of light radiation or a radiation similar thereto and by means of a radiation receiver in which a slit aperture and the surface bearing the deformations are arranged at such a distance from one another that a change results at the slit plane in the density, of the radiation emanating from the surface bearing the deformations. This change depends on the curvature existing in the direction of the relative speed of the carrier with respect to the reading beam, which change in density, at least'qualitatively, represents the shape of this curvature. The signal value is here a recorded carrier oscillation which is frequency or phase modulated by the recorded signal.

This process retains the advantages of the stamping or pressing copying technique, as it is used in the manufacture of phonograph records. Since light scanning is used, the scanning is free of mass inertia which is unavoidable with scanning by means of mechanical sound pickups which come in contact with the groove. Also the surface of the carrier bearing the signal recording is not subject to any mechanical stresses.

In this latter process use is made of the fact that the deformations constituting the signal recording form convex or concave lenses, or convex or concave mirror surfaces, which cause the preferably collimated light of the reading beam to be density modulated in the slit plane in accordance with the course of the curvature of the surface. This density modulation is a qualitative representation of the effective surface curvature in the ing surface of the carrier. In this case a concave surface "produces a collection effect with resulting increase in the light density and a convex surface produces light dispersion with resulting decreasein the light density in the slit plane.

In order to maintain constant the distance of the plane of optimum convergence of the light coming fromt'he reading beam bundle the signal is recorded as already mentioned as a carrier oscillation which is frequency or phase modulated with the signal. Thus the wavelengths of the deformations containing the signal recordings need be variable to a lesser degree than would be required with direct recording of a lowfrequen'cy band having a large bandwidth. If any desired frequency oscillation were recorded directly in the deformations, the wavelengths and amplitudes of the deformations would vary widely for the individual components of such a complex signal. This would result in generally different curvatures and thus different focal "widths for the cylindrical lenses or cylindrical mirrors so that the plane of optimum convergence of the radiation taken from the reading beam bundle would 'lie at different distances from the surface plane for the different wavelengths or amplitudes, respectively.

By recording such signals by means of frequency or phase modulation of a carrier oscillation the amplitude of the recorded signal values can be maintained approximately constant and the range of fluctuation of the wavelengths with respect to a mean wavelength is substantially reduced. Under these circumstances a certain distance of the slit plane from the mean surface plane of the carrier provided with the deformations can be defined as being the optimum distance.

SUMMARY OF THE INVENTION In the process according to the present invention the signal carrier employed is preferably of the type on which a carrier oscillation which has been frequency or 'phase modulated with the signal is recorded by mechanical means. However the present invention is also adapted for use with a signal carrier having a directly recorded signal frequency.

Contrary to the above-mentioned known process however, the process according to the present inven- 'tion employs a very narrow beam of radiation which is narrower than the wavelength of the highest recorded frequency. Accordingly, the present invention relates to a process for reproducing stored signals from a carri'er whose surface is provided with deformations corresponding to the time pattern of the signal amplitude, these deformations being evaluated by means of light radiation, or a radiation similar thereto and is charac terized in that a beam of light or other radiation is used for scanning. The width of this beam at the locus of the modulated carrier surface as seen in the direction of movement of the carrier is approximately equal to or narrower than one-half of the shortest recorded wavelength. I

The present invention contemplates the use of a transparent carrier in the form of a disc with a spiralshaped signal track which is scanned with a light beam passing through the carrier. It is also possible, however, to use a tape-type carrier whose surface is provided with deformations, as is the disc, which correspond to the time patterns of the signal amplitude.

Instead of transmitted light scanning it is also possible to use reflection scanning, where it would be advisable, however, to cut the groove bottom, in vertical recording, and thus the upper or lower portions, respectively, of the deformations, which are parallel thereto, somewhat at an angle to the carrier foil plane so that the reflected beam does not coincide with the transmitted beam.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. la, lb, and 1c are cross-sectional detail views showing diagrammatically how a light beam passing through a carrier, with a signal recorded thereon, is deflected toward a photoreceiver and a half plane aperture as the carrier moves from right to left.

FIG. 2 is a waveform diagram showing the form of the electrical output signal derived from the photoreceiver as the carrier moves in the manner shown in FIGS. la, lb, and 1c.

FIGS. 30, 3b and 3c, show a series of figures similar to FIGS. la, lb and 1c, but in which the lateral dimension of the light beam is equal to one-half wavelength of the recording frequency.

FIG. 4 shows the output of the photoreceiver 4 as the carrier 2 moves in the sequence shown by FIGS. 3a, 3b, and 3c.

FIG. 5 is a cross-sectional detail view showing the use of a focused beam in conjunction with the carrier, the photo-receiver, and the half plane aperture.

FIG. 6 is similar to FIG. 5, but shows a triangular modulation of the carrier surface.

FIG. 7 shows a slit aperture arrangement according to the invention.

FIG. 8 showsa cross-sectional detail view similar to FIG. 30, but in which two photoreceivers are provided.

FIG. 9 shows a push-pull circuit for the electrical signals produced by the photoreceivers of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. la to It and 2 serve to explain the idea on which the present invention is based. The signal is assumed to be recorded in a vertical recording, and is for example frequency modulated. A light beam 1 which passes through carrier 2 is employed for scanning the modulations. Its transverse dimension in the direction of the relative movement is initially assumed to be small compared to the wavelength. Due to the differences in reflection at the deformed surface 3, the beam 1 is periodically deflected toward the left and right during the relative movement between carrier 2 and the light source as indicated by the arrows pointing toward the left.

As carrier 2 moves in the direction of the arrows, the beam 1 periodically impinges on a photoreceiver 4 which in the ideal case furnishes the electrical output signal shown in FIG. 2. The curve path is plotted to show signal S in dependence on time t. Time 21.

corresponds to the position of carrier 2 as shown in FIG. In, time t corresponds to-that of FIG. lb and time to that of FIG. 1c. During one half-period the beam impinges on the light-sensitive surface of receiver 4 and during the other half it impinges on a covering or half plane aperture, 5. S is the dark signal, e.g. dark current, of receiver 4.

In a practical case various changes result for the output signal when compared with the theoretic curve of FIG. 2. Forexample, the lateral dimension of the beam is not arbitrarily small compared to the wavelength. Attention is directed to FIGS. 3a, 3b, and 3c where the light beam 6 covers, for example, one-half wavelength of the recording, but is still intended to represent a collimated light beam. In this case the deformation of the carrier surface results in a light dispersion as shown in FIG. 3 for three characteristic times in a period which correspond to those of FIGS. la-lc. In this case the signal resulting at the output of the photoreceiver 4 is shown in FIG. 4 and is approximately triangular. If, which will always be the case in practice, the distance between carrier 2 and photoreceiver 4 is large compared with the transverse dimension of the light beam 6, the signal minima S will approach the value of the dark signal S If the light beam has a smaller transverse dimension than half the wavelength (M2) of the highest recorded frequency, the signal path will approach the rectangular shape of FIG. 2. If it is wider than M2, the signal dark value S will no longer be reached. While the mean value of the signal increases, the alternating component, which represents the actual useful signal, drops and entirely disappears at a beam width of A, 2A, 3A, .etc.

In a further case occurring in practice the beam 6 may have a finite width and an aperture angle which is greater than zero, for example 15. This is disclosed for the focused beam shown in FIG. 5. Care must first be taken that the beam width at the locus, i.e. median plane, of the modulated surface is no greater than M2 if possible. If a focused beam is employed, this means that the focal point must lie very close to the modulated surface. This produces a different situation as compared to the case of a collimated beam because some of the marginal rays cannot be deflected into the desired direction. With a beam width of M2 at the locus of the modulated surface, such a focused beam thus produces a reduction in the alternating component in the output signal of the photoreceiver. The reduction is the more distinct, the wider the aperture angle of the beam. In this case an improvement can be realized by a triangular modulation of the carrier surface as shown in FIG. 6.

The narrow light beam required in reducing the present invention to practice can be produced, for example, by converging a broader light beam, e.g. a laser beam, by means of a lens having a long focal length. The focused beam then has a small aperture angle. A further possibility of producing the light beam is to reproduce a slit aperture by means of an optical system which again imparts a small aperture angle to the light beam impinging on the carrier.

These two possibilities of producing a narrow light beam require the maintenance of a certain distance between lens and carrier surface so that sharp focusing or reproduction on the carrier surface is maintained. When scanning a disc-shaped foil having a helical signal track which undergoes height variations while rotating rapidly, the maintenance of a sharp reproduction is difficult. Added to this is the further difficulty of maintaining the track when the foil experiences any marked degree of radial wobble.

These difficulties can be avoided, according to a further embodiment of the present invention, in that the light beam is brought to a slit aperture whose exit side is disposed directly adjacent the modulated carrier surface. If the modulation is recorded in a spiral groove, as is the custom for disc-shaped carriers, the groove itself may be used as the slit aperture.

Advisably the slit aperture is constructed as a light conductor as already proposed, and it is recommended that it be suspended elastically so that it can follow the track when the carrier foil undergoes a vertical or lateral wobble.

One embodiment of such an aperture and its arrangement in the beam path is shown in FIG. 7. The light permeability of a slit depends not only on its crosssectional dimensions, i.e. therectangle in the illustrated embodiment, but substantially also on its depth, particularly when the radiation does not always impinge perpendicularly on the slit entrance aperture.

To produce as few reflection losses as possible at the border surfaces of the gap there are several possibilities. Of these metallic mirror-plating of the boundary surfaces should first be mentioned. Since the reflection capability of metallic mirrors is no more than 0.96 to 0.98, a twenty-fold reflection will already produce a loss of more than 50 percent. Such mirror-plating is useful, therefore, only when the slit depth is no more than twenty times the slit length. This requirement makes the fabrication of such a slit relatively difficult.

A more advantageous possibility consists in the utilization of the phenomenon of total reflection at the boundary surfaces. In this case, the loss of light due to reflection is very low so that even after several thousand reflections the intensity loss will only be very slight. Prerequisite for the occurrence of total reflection is that the medium of the slit be optically denser than the surrounding medium.

In the embodiment shown in FIG. 7 the slit is formed by a solid light-conducting slit member .7 which is permanently connected at its lateral boundary surfaces 8 with the adjacent portions of a guide member 9 by an adhesive 10. For the slit member 7 a material is used whose index of refraction is such that total reflection will result at the bordering planes 8 in the useful range of the optical angles of incidence at the slit entrance. In this case the slit depth may be selected to be substantially larger than would be possible if no advantage were taken of the total reflection phenomenon.

The necessary optical condition for achieving total reflection is that the material of the slit member 7 be optically denser than the surrounding medium 10. A glass foil serving as the slit member which has a high index of refraction, e.g. in 1.7, is inserted with the aid of an adhesive 10 or by means of a glass solder having a lower index or refraction, e.g. n 1.5, into an opening in the opaque guide member 9. The slit member 7 then acts as a light conductor for all the light impinging on the slit entrance surface at an angle, in the case of the above-mentioned indices of refraction, of 37 to 90. Even when the difference between the indices of refraction is only 0.1, the usable angular range is still sufficiently high for the impinging light beams.

.FIG. 7 also shows the arrangement of the slit aperture in the beam path, generally indicated at 11, and produced from a light source, not shown. It is placed as close as possible to carrier 2. The useful light beam leaves the slit at the same angle at which it enters the slit. The photoreceiver 4 is relatively far removed from the carrier surface. Thus as in the case of FIGS. 3a-3c almost the entire light beam is utilized or covered by the half plane aperture 5. The loss of light is then infinitely small.

On the exit side of the slit the light will be dispersed, or diffraction will occur. This means that even with the light entering the slit aperture in the form of a perfectly collimated beam, it will exit at an aperture angle which is greater than zero. For a slit width of 1.5 to 2n, the aperture angle for the major portion of the light will be 2a 10 to 15. The aperture angle becomes smaller as the wavelength of the light used is reduced.

Generally it will have to be taken into account that the lightemployed for illuminating the slit will not impinge exactly in the direction of the slit. This deviation leads to an increase in the angle of the exiting light beam.

The total aperture angle should be kept as small as possible. An aperture angle 2a 20 to 25 is realizable without too much trouble for a slit width of approximately 2,u.. The distance of the light exit side of the slit aperture from the carrier surface should only be great enough that no substantial widening of the light beam takes place between the slit exit and the carrier surface. With a wavelength of e.g. 4 .L and sinusoidal modulation, the alternating signal component will then decrease only slightly at the output of the photoreceiver for a slit exit-carrier surface distance of 2a when the slit width is less than M2, where )t is the shortest recorded wavelength, and the exit angle of the light beam is less than 20.

It is particularly advantageous to use short-wave light, e.g. blue light or ultraviolet light, since this permits the realization of a sharp delineation of the light beam exiting from the slit aperture. Moreover, conventional photoreceivers have a high sensitivity in these wavelength ranges. In place of the half-plane aperture 5 illustrated in the drawings, a second photoreceiver may be provided for better utilization of the light, which receiver permits a push-pull connection with the first photoreceiver.

FIG. 8 shows an arrangement similar to that of FIG. 3c, but in which two photoreceivers 11 and 12 are provided. If during scanning the part of the light beam received by one of the photoreceivers becomes greater the other part received by the other photoreceiver becomes narrower. This allows to use a push-pull circuit as shown scematically in FIG. 9. The cathodes of the photoreceivers 11 and 12 are connected to the negative terminal of a power source U. The anodes are connected to the primary winding of a transformer 13. The centre tap of the primary winding is connected with the positive terminal of the power source U. The electrical signals corresponding to the recorded signals at the surface 3 of the carrier 2 in FIG. 8 appear at the terminals 14 and 15 of the secondary winding of the transformer 13.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. Apparatus for reproducing stored signals from a carrier whose surface is provided with spatial deformations corresponding to a carrier oscillation angularly modulated with the stored signal, the deformations serving to deflect a radiation beam impinging thereon, comprising, in combination: source means for producing a radiation beam which is directed toward the region where the deformations of the carrier will be located during signal reproduction; means for moving the carrier relative to said source means so that said radiation beam progressively scans the deformations; means for directing said radiation beam to progressively sweep over a limited portion of the deformations; an associated radiation receiver having a radiationsensitive surface exposed to only that portion of the scanning radiation beam emanating from the carrier, which is to one side of the axis of the beam as it is directed to the carrier, so that said receiver receives only such beam portion, for producing signals corresponding to the stored signal; and means for limiting the width of the radiation beam at the location of the median plane of the deformations, in the direction of movement of the carrier, to a value which is no greater than one-half of the shortest recorded wavelength.

2. Apparatus as defined in claim 1 further comprising a half-plane aperture disposed for blocking the transmission of a portion of the radiation beam, which emanates from a deformation, to said radiation receiver.

3. Apparatus as defined in claim 1, further comprising: a second radiation receiver having a radiationsensitive surface exposed to only that other portion of the scanning radiation beam emanating from the carrier, which is to the side of the beam axis which is opposite to said one side thereof, so that said second receiver receives only such other beam portion, for producing signals corresponding to the stored signal; and a push-pull circuit connected to combine the outputs of the respective radiation receivers to produce signals corresponding to the stored signal.

4. Apparatus as defined in claim 1, wherein said directing means and said limiting means are constituted by a slit aperture which is closely positioned adjacent the location of the deformations during signal reproduction and the width of said slit aperture, in the direction of the relative movement of the carrier, is no greater than one-half of the shortest recorded wave length.

5. Apparatus as defined in claim 4, wherein the deformations are in a spiral groove in the carrier surface, and said slit aperture is resiliently mounted to be guided in said groove.

6. Apparatus as defined in claim 4, wherein said slit aperture means is constituted by a solid, transparent slit body member, an opaque guide member, and an intermediate layer permanently connecting said body member with adjacent portions of said opaque guide member.

7. Apparatus as defined in claim 6, wherein said slit body member has a higher index of refraction than said intermediate layer so that total reflection results in the useful area of the radiation along the lateral bounderies of said body member.

8. Apparatus as defined in claim 7, wherein said slit body member is a glass foil.

9. Apparatus as defined in claim 7, wherein said glass foil is connected with said guide member by means of an adhesive constituting said intermediate layer. 

1. Apparatus for reproducing stored signals from a carrier whose surface is provided with spatial deformations corresponding to a carrier oscillation angularly modulated with the stored signal, the deformations serving to deflect a radiation beam impinging thereon, comprising, in combination: source means for producing a radiation beam which is directed toward the region where the deformations of the carrier will be located during signal reproduction; means for moving the carrier relative to said source means so that said radiation beam progressively scans the deformations; means for directing said radiation beam to progressively sweep over a limited portion of the deformations; an associated radiation receiver having a radiation-sensitive surface exposed to only that portion of the scanning radiation beam emanating from the carrier, which is to one side of the axis of the beam as it is directed to the carrier, so that said receiver receives only such beam portion, for producing signals corresponding to the stored signal; and means for limiting the width of the radiation beam at the location of the median plane of the deformations, in the direction of movement of the carrier, to a value which is no greater than one-half of the shortest recorded wavelength.
 2. Apparatus as defined in claim 1, further comprising a half-plane aperture disposed for blocking the transmission of a portion of the raDiation beam, which emanates from a deformation, to said radiation receiver.
 3. Apparatus as defined in claim 1, further comprising: a second radiation receiver having a radiation-sensitive surface exposed to only that other portion of the scanning radiation beam emanating from the carrier, which is to the side of the beam axis which is opposite to said one side thereof, so that said second receiver receives only such other beam portion, for producing signals corresponding to the stored signal; and a push-pull circuit connected to combine the outputs of the respective radiation receivers to produce signals corresponding to the stored signal.
 4. Apparatus as defined in claim 1, wherein said directing means and said limiting means are constituted by a slit aperture which is closely positioned adjacent the location of the deformations during signal reproduction and the width of said slit aperture, in the direction of the relative movement of the carrier, is no greater than one-half of the shortest recorded wave length.
 5. Apparatus as defined in claim 4, wherein the deformations are in a spiral groove in the carrier surface, and said slit aperture is resiliently mounted to be guided in said groove.
 6. Apparatus as defined in claim 4, wherein said slit aperture means is constituted by a solid, transparent slit body member, an opaque guide member, and an intermediate layer permanently connecting said body member with adjacent portions of said opaque guide member.
 7. Apparatus as defined in claim 6, wherein said slit body member has a higher index of refraction than said intermediate layer so that total reflection results in the useful area of the radiation along the lateral bounderies of said body member.
 8. Apparatus as defined in claim 7, wherein said slit body member is a glass foil.
 9. Apparatus as defined in claim 7, wherein said glass foil is connected with said guide member by means of an adhesive constituting said intermediate layer. 